This invention relates to methods of inducing dendritic cell formation and methods of using induced dendritic cells as therapeutic agents.
Dendritic cells (DCs) are important decision makers within the immune system. For example, DCs initiate adaptive immune responses such as antibody production and killer cell formation. DCs also direct the quantity and quality of immune responses, for example determining whether an allergic, inflammatory, or tolerogenic immune response is to be mounted.
Many phenotypically and functionally distinct subsets of DCs exist (1). Though they are rare in the blood and immune organs, DCs include two major subgroups of different subsets, the plasmacytoid DCs (pDCs) and the conventional DCs (cDCs) (2). The cDCs in mouse include at least 3 subsets: CD4+CD8−, CD4+CD8− and CD4−CD8−. The CD8+ cDCs express the surface marker CD8αα and are the most important cells for cross-presentation of antigens, which allows for killer cell induction against viral infection. The CD8+ cDCs can also produce large amounts of of interleukin-12, an essential cytokine for inflammatory immune responses. The CD8− cDC populations are known to produce large amounts of chemokines and to be better at MHCII presentation of antigens to T cells. pDCs are anti-viral cells, that produce large amounts of the anti-viral and immune protecting cytokines, including type I Interferons (IFN-I) in response to viral DNA or viral RNA.
Like other immune cells, DCs develop from haematopoietic stem cells and later stage precursors under the influence of growth factors and cytokines. Granulocyte-Macrophage-Colony Stimulating Factor (GM-CSF) induces haematopoietic precursor cells and monocytes to develop into DCs, called GM-DCs (3-5). GM-DCs are not the majority of steady state DC subsets in lymphoid organs, though, since mice deficient for either GM-CSF or the GM-CSF receptor do not demonstrate much impairment in DC numbers (6). However, application of stabilized GM-CSF to mice in vivo results in increased levels of CD8− cDCs, but not pDCs (10). Moreover, GM-CSF has been shown to block generation of pDCs in vitro (7).
Fms-like-Tyrosine-Kinase 3-Ligand (FL) also induces development of DCs, including both cDCs and pDCs, from bone marrow (BM) precursor cells (8,9), both in vitro and in vivo (10-13). The role of FL in development of DCs (called FL-DCs) has been definitively demonstrated by the drastically reduced number of both pDCs (9) and cDCs (14) in the lymphoid organs of mice deficient in FL (FLKO).
Ex vivo isolated or FL-generated pDCs respond to direct stimulation via the Toll like receptors (TLR) 7 and 9 and their respective ligands, RNA and DNA, by producing high levels of Interferon-alpha (IFN-α). Other cell types, including cDCs, can be induced to produce IFN-α in response to active viruses or transfected DNA or RNA. IFN-α production by cDCs, though, is mediated via TLR7 and TLR9 independent pathways, including PKR, RIG-I, MDA5 and TLR-3 and as yet unidentified cytoplasmic DNA-recognition complexes (15-17). Thus, pDCs are the only cells that employ TLR7 and 9 for the high level production of IFN-α. Furthermore, certain nucleic acid molecules, such as CpG-motif containing oligonucleotides (CpG-ODN A-type), induce extremely high levels of IFN-α solely in pDCs (18). Therefore, IFN-α production in response to A-type CpG-ODN is a functional test for the presence of pDCs in mixed cell populations (17).
From studies employing GFP encoded downstream of the receptor for Macrophage Colony Stimulating Factor (M-CSF; also called CSF-1), it is clear that during differentiation of pDCs and cDC subsets the M-CSF receptor is transcribed (26). In addition, there is a report that mice deficient in M-CSF (op/op mice) have reduced numbers of DC subsets (26). Furthermore, DCs and macrophages may develop from a common progenitor cell (41). Other reports show that some DCs, though not pDCs, develop under the influence of a combination of growth factors, including M-CSF (42). Nevertheless, while GM-CSF and FL have been shown to induce development of DCs, M-CSF has always been considered to induce development of monocytes and differentiation of macrophages, not DCs (34).
The effect of M-CSF as a therapeutic treatment has previously been investigated, though in limited situations, such as in the treatment of invasive fungal infections (39). It is not known if the patients treated with M-CSF displayed any changes in their DCs.
An increase in the number of DCs could be therapeutic in certain situations. For instance, more DCs would be helpful in fighting infections in neonatal individuals. Similarly, individuals who suffer from HIV infection, certain cancers, allergies, have received transplants or who are immunocomprimised due to radio or chemotherapy or from taking certain drugs may have reduced numbers of DCs. In these individuals, it would be desirable to increase the numbers of DCs, including pDCs and cDCs. Thus, there is a need in the art for methods of DC induction, either in vitro or in vivo.